What if a dairy sponge was used to wash meaty plates by accident by a goyish cleaning lady. The plates washed were ceramic, do I need to throw out the plates?
No, under the circumstances there is no need to throw out the plates.
We do not know that the water used was hot. Moreover, even if hot, if detergent was used the taste absorbed by the sponge becomes “pagum,” and therefore will not impart taste to the plates. It is also possible that the sponge was not used recently for meat (perhaps you know this).
For these reasons one can be lenient and the plates are fine.